3He

Helium 3 is a rare isotope of the element Helium, consisting of a nucleus with two protons and one neutron. The approved abbreviation (for physics use) for Helium-3 is 3He, however, the abbreviation He3 is also seen. Since most of the Earth's helium is produced by alpha-decay of Uranium isotopes, resulting in 4He (the most common isotope of Helium), 3He is rare on Earth. It is comparatively more abundant in non-terrestrial sources, although even in non-terrestrial sources, only a small fraction of helium atoms are Helium 3. The Moon is a source of 3He, which is implanted into the lunar regolith by the solar wind. Helium is present in the soil in quantities of ten to a hundred (weight) parts per million, and 0.003 to 1 percent of this amount (depending on soil) is 3He.

Helium 3 as a Fusion Reaction Fuel

It has been proposed that 3He might be a possible fuel for a Nuclear Fusion reactor to produce energy using the thermo-nuclear reaction (Deuterium-Helium-3):

2H + 3He --> 4He + 1H+

This reaction has the advantage over the more-commonly proposed Deuterium-Tritium fusion reaction

(2H + 3H) --> 4He + Neutron

that the reaction produces only charged particles (an alpha particle and a proton), with no production of neutrons. However, the corresponding difficulty is that the 2H -3He reaction has an ignition barrier that is twice as high as the barrier to igniting 2H-3H fusion, because of the fact that the Helium nucleus has twice the charge of a Tritium nucleus. Gerald Kulcinski's group at the Fusion Technology Institute of the University of Wisconsin-Madison has operated an experimental 2H-3He fusion reactor for an extended period, on a non-governmental research budget [1], however the reactor has not achieved energy balance or "break even". So far, 2H-3He fusion has not yet demonstrated net energy production ("break even"). The development of commercial 2H-3He reactors is dependent upon demonstrating "break even."

Helium 3 Fusion and a Lunar Settlement Window

Mining Helium 3 from the lunar regolith for generation of power on Earth is a very attractive economic foundation for a lunar settlement economy. A number of powerful historic forces are pushing the human race in this direction, but the hurdles that must be overcome are daunting.

Human civilization needs a source of electrical power to maintain itself. Currently we are running on fossil fuels that are a limited resource and dump of huge amounts of greenhouse gases into Earth's atmosphere. Even given the immense effort that it will take to develop fusion as a power source, fusion is currently one of our best possibilities for addressing the global warming problem.

Current fission reactors will not meet 21st century needs. They are limited by the possibility of nuclear proliferation, safe handling of the radioactive wastes, the amount of high grade ore available, and problems with the decommissioning of radioactive power plants at end-of-life.

There are several possible fusion fuels (Deuterium, Tritium, Helium 3, and Boron 11) that could be used. Only one, Helium 3, comes from the Moon.

Each fuel has different prospect for use. The relative economic values can be judged by: (1) ease of ignition, (2) possibility of power generation, and (3) safety of wastes produced. Three of the top five possibilities are rated below:

Fuel

Lawson Criterion

Relative Power Density

Neutronicity

Deuterium-Tritium

1

1

0.80

Deuterium-Helium 3

16

80

0.05

Proton-Boron 11

500

2500

0.001

The Lawson Criterion is a index of how difficult the reaction is to initiate with respect to the Deuterium-Tritium reaction. The Relative Power Density gives an idea of how much power might be harnessed commercially. The Neutronicity shows how much of the energy produced comes off in the form of fast neutrons which produce most of the radioactive wastes.

This basic comparison suggests a possible economic window of opportunity for lunar Helium 3 mining. The easiest fusion fuel, Deuterium-Tritium, comes from the seas of Earth, but the Tritium must be produced in conventional fission reactors and the fusion facility would slowly become radioactive and turn into a huge pile of radioactive waste after about 40 years of operation.

The Helium 3 reaction is more difficult to initiate, but produces more energy with each reaction and produces negotiable radioactive wastes. Its problem is that the bulk of Helium 3 will have to be mined on the Moon at great cost.

As fusion technology progresses, we will likely someday be able to fuse Boron 11. This is far more difficult to do, but yields far more energy while generating truly negotiable radioactive wastes. All this fuel's constituent parts are available at low cost on Earth.

This suggests a window of opportunity for a lunar Helium 3 mining settlement. The following historic events need to take place to open this window: (1) it is determined that dumping carbon dioxide into Earth atmosphere must be stopped no matter what the cost, (2) wind and solar are not up to the job alone, (3) Deuterium-Tritium power production is accomplished, (4) Deuterium-Helium 3 power production is demonstrated, and (5) we build a lunar mining settlement. There is nothing unreasonable in this list, although there is also nothing certain.

This window would start to close when commercial Boron 11 fusion is demonstrated. The established lunar settlement will then have to find other means of economic support.

Value of Lunar Helium 3 in Today's Market

Since He3 has a high market value today, it might be worth collecting He3 from the Moon today simply to sell into the existing terrestrial market.

Demand for Helium-3 is steadily increasing primarily for Neutron detectors for cargo screening (for illegal fissile material).
In 2008, a total of 80,000 liters of He3 were sold worldwide, at an average price of $100 per liter, i.e. total market of $8 million. Then starting 2009 the DOE has introduced rationing and the price jumped dramatically.

In 2010 DOE released 14,000 liters per year, at a spot market auction price of $2,000 per liter, $15,000 per gram or $500,000 per troy ounce, over 300 times the price of gold or platinum by weight.

Questions:

Can the cost of recovering He3 from the lunar surface be reduced to that level, e.g. $15K per gram?

What would be the capital cost of setting up a small He3 production facility on Luna?

Would it depress the market price today? This depends on the size of the market, and there is little data.

The US Tritium and helium-3 stockpile sizes were classified until 2010, because they give a hint as to how many US nuclear weapons are still functional. When it was declassified, there was a shock because the stockpile was much smaller than anybody realized, and at the same time global demand was rising and there were only a few years of supply left, so rationing was introduced.

The cost of soft landing even a small probe on to the lunar surface may easily cost more than $200M. How much He3 a small lander would manufacture and how many grams per day have yet to be determined. Production will be determined by the method of processing.

A commonly discussed method is cooking the regolith to about 1400 degrees Fahrenheit or 760 degrees Celsius[2]. They describe three steps:
1) heat to a few hundred deg C to drive off the volatiles 2) fractional distillation to decant off the heavy volatiles 3) separate He3 from the He4 using the standard superleak process. Two challenges are devising a method to process large quantities of regolith as the He3 is at a low concentration, and providing a high power thermally efficient heat source on the Moon. This would need a large amount of energy, requiring the lander to have either a nuclear source (either Nuclear Fission or RTG), or large solar panels. Basalt has specific heat capacity of 0.24 cal/g/degree C or 0.84 KJ/kg degree K. To heat 1kg of basalt by 700 degrees Celsius requires about 600 KJ. The highest concentration of He3 in the Maria regions is 0.01ppm in the regolith. This means that 600 KJ will yield 0.01 milligrams of He3. Using these numbers, a 600 Watt power source could produce 0.01 milligrams of He3 per second = 0.6 mg/minute = 36mg/hour = 864mg/day = 315 grams per year. Whether this business concept is viable depends on how quickly a group or entity wants to amortize their investment. If an arbitrary target is to produce 100 kg He3 in one year, then a power source of about 200 KW would be needed. That would give a revenue stream of $400M per year if the He3 market does not become flooded causing a price drop.

A Solar Power based system would be in darkness 50% of the time, so would need to operate at 400 KW. If it were on a lunar polar mountain top it might be in near continuous illumination. Assuming a best case scenario of 100% lighting, 10% photo voltaic efficiency and a fully steerable array, this would need an area of about 2,000 square meters, or about 45 meters on a square side. A simple non-PV solar reflector could be near 100% efficient, needing only 200 square meters or about 14 meters on a square side, or aperture. Setting up a 14 meter aperture mirror on the Moon would be a major engineering challenge, although it would not need to be particularly accurate as in the case of an astronomical telescope mirror.

Open Questions:

How much would a 14 meter aperture mirror weigh?

Would a Nuclear Fission power plant have better performance per kilogram of lander payload?

More thermal analysis needs to be done, as it may be possible to recycle the heat using some form of cogeneration. One possibility is to use the hot processed regolith to pre-heat the next incoming batch of raw dust, and thus reduce the number of solar joules needed. This could greatly reduce the size of solar array needed and/or significantly increase the system mass throughput.

Chronic shortage of Helium-3 isotope could be resolved by mining lunar regolith

In 2008, a total of 80,000 liters of He3 were sold worldwide, at an average price of $100, i.e. total market of $8 million -

Then starting 2009 the DOE has introduced rationing,

In 2010 DOE released 14,000 liters per year, at a spot market auction price of $2,000 per liter (US government customers received subsidized prices). This is a proven global market of around $28 million, perhaps more if we include non US DOE sources, e.g. in Russia.

The market could expand to say $50 million or even $100 million per year if plentiful lunar He3 comes on line (price TBD).

There is a critical shortage of He3 today, due to two factors:

1) increasing demand for neutron detectors since 2001 for cargo screening at airport and seaports. There is also increasing demand at research facilities.

2) reduced supply due to decommissioning and destruction of nuclear warheads in USA and Russia

Table-3 in the preceding ref shows Helium-3 price trends steadily increasing. The spot price has more than doubled in the last 3 years (2009 though 2011). The stockpiles of He-3 are shrinking rapidly, and there are only a few years of supply left in the current stockpiles, at which point the price could jump by orders of magnitude.

One alternative terrestrial source is extracting He3 from natural gas. It could cost $12,000 per liter.

The commercial amount of He3 needed would be 10,000 liters per year to 100,000 liters per year. He3 density is about 0.1g per liter at NTP, so we need about 1kg to 10 kg of the gas per year. At average concentration about 150,000 tons of regolith per year would need to be processed. About 500 tons per day, 22 tones per hour

Markets consider upside pressures and downside pressures.

Helium-3 is a very unusual commodity, in that presently it is completely synthetic, and the Helium-3 traded has not been occurring in nature.

We have been feeding off of the nuclear warhead stockpile which has been the source of all the He3 in the world... that warhead stockpile is now mostly gone, so the rate at which we can replenish the He3 stockpile has dropped off a cliff

We are now left with a known finite stockpile of He3 which is shrinking at a known rate.

Unlike most commodities, we know exactly how big the He3 stockpile is, and we can track how it is being consumed.

The stockpile is now down to about 50,000 liters, and the US DOE is presently releasing it at about 14,000 liters per year, and replenishing it with 8,000 liters per year.

Since natural demand has been demonstrated at 80,000 liters per year (2008), DOE is implementing a form of strict rationing, to try and eke out the He3 stockpile as long as possible.

There is a shortfall of 80,000 minus 14,000 liters = 66,000 liters of pent up demand, or to put it another way, the existing supply of He3 can only satisfy 17.5% of world demand.

The obvious terrestrial solution to the He3 supply problem is to make more tritium in the same way that it was made for nuclear weapons and then let it decay to He3. A blanket of lithium six is placed in the neutron flux outside the core of a nuclear reactor. Tritium is generated in the lithium. If there is a market for He4, that would be a by-product.

At present the US Government is investing heavily in Boron-10 technology as a second rate alternative to Helium-3 for neutron detectors.

According to Harrison Schnmitt in his 2006 book "Return to the Moon", the Mark-II lunar miner of the Wisconsin University Fusion Institute, would cost about $1 billion. This Mark-II plant would produce 33 kg of He3 per year. This is several times more than needed to service the existing terrestrial He3 market .... presumably we could build a plant to produce 10 kg per year for $500 million?